I can't speak too much for DTV specifically...but in general amplified antennas are bad news. There is no magical way to increase signal level other than having higher antenna gain. And the only way to achieve that is a bigger antenna with more surface area. Try your local Radio Shack, they have a decent UHF antenna that's rear-mount directional for about $30. Admittedly, it'd be a bit unwieldy and ugly in your living room, but it's not so huge that it'll be THAT obnoxious outside.
Amplifiers may raise the signal but usually they just raise the noise floor right along with it; the end result is worse because a good tuner can get a weak-but-clean signal, but no tuner can handle tons of noise.
Terrain matters with UHF...a lot. In general, the higher the frequency, the more susceptible to terrain interference it becomes. That's why most of the REALLY tall towers were originally built by/for TV stations. And UHF is the highest freq's for TV. So if there's any way to get your TV antenna up on your roof, that might help a great deal...especially if it's above the treeline (or close to above it).
Also, some amplifiers don't amplify the right frequencies. HD Radio is not DTV and vice-versa, but I know of some "amplified HD Radio" antennas that don't have enough bandwidth to properly pass the IBOC carriers...so this "HD Radio" antenna will actually make it near-impossible to receive HD Radio.
